In recent years, for example, hybrid vehicles or electric vehicles have been developed as vehicles for protecting the environment. These vehicles include a motor as a driving source. There is a vehicle including a plurality of motors (motor generators or generators). An AC motor is used as the motor and an inverter converts DC power into three-phase AC power. The motor is driven by the three-phase AC power. A high voltage is needed in order to rotate the motor at a high speed or with high torque. A boost converter is used to boost the DC voltage of a battery to a DC high voltage and the DC high voltage is supplied to the inverter. Therefore, in the vehicle, inverter control for controlling switching between switching elements of the inverter and boost control for controlling switching between switching elements of the boost converter are performed in order to control the motor. A smoothing capacitor is provided between the boost converter and the inverter and a voltage sensor detects the voltage (DC high voltage boosted by the boost converter) between both ends of the smoothing capacitor. In the boost control, the DC high voltage detected by the voltage sensor is used to obtain a target voltage required to drive the motor. In particular, a system including a plurality of motors sets the target voltages required to drive the motors and selects a target voltage of the system from a plurality of target voltages.
Patent Literature 1 discloses a vehicle control device including two motor generators. The vehicle control device generates a gate signal for controlling switching elements of a boost converter on the basis of the sensor value of the voltage from a DC power supply, the sensor value of the voltage between both ends of a smoothing capacitor, a motor torque command value of each motor generator, and the number of rotations of the motor, and generates a gate signal for controlling switching elements of an inverter in each motor generator on the basis of the sensor value of the voltage between both ends of the smoothing capacitor, a motor torque command value, and the sensor value of a motor current.